When patients emerge from general anesthesia after a lumbar spinal procedure they often go into lumbar muscle spasms as a result of the incisional pain combined with the abrupt loss of effective lumbar analgesia. This combination often leads to the creation of a pain spasm cycle of the lumbar muscles at the incisional wound area where the local muscle spasms cause more incisional area pain, which then cause more local muscle spasms and even more pain. Often intravenous narcotics and benzodiazepines are required to break this cycle which can last from thirty minutes to hours and in severe cases even days. This pain spasm cycle is not only quite uncomfortable to the patient but additionally prevent many patients with a smaller procedure such as a discectomy or laminoforaminotomy (typically the L4-L5 or L5-S1 level and occasionally the L3-L4 level) from going home on the day of surgery. Although, the true cost of a patient staying an extra day varies wildly depending on the region and insurance contract with the hospital, it is fair to assess the true cost in the $1000.00 to $2000.00 range. Thus there is an obvious advantage to insuring that the patients are comfortable with good pain control so that they can go home as same day surgery. The current therapy of a combination of intravenous and oral medication in the postoperative period have proven unable to prevent the incisional area pain and/or leg pain from triggering the pain spasm cycle in the majority of patients.
Three types intraoperative locally applied analgesia are available that could be implemented in an effort to prevent this pain spasm cycle:
1. Local can be Injected into the Muscle and Skin. An injection of ¼% Sensorcaine injected into the skin only just prior to skin closure in addition to before the initial skin incision carries no risk of intradural injection while providing a level of incisional analgesia. However, this superficial analgesia usually only provides incomplete pain management because the deep wound musculature structures nor the ligaments around the facet joint and posterior longitudinal ligament are not covered by the superficial injection in the skin. These deep structures cannot be adequately injected without risk of intradural injection. An intradural injection can result in various medical problems including life threatening seizures and reversible paralysis sometimes requiring a ventilator for temporary support. An intradural injection will insure that the patient will not be discharged on the day of such an injection. Additionally the total muscle that is surgically injured (painful in the postoperative period) is not only the muscle disconnected for the bone visually seen in the surgical incision but all the muscle stretched for the necessary surgical retraction. This stretch injured muscle tissue can be over 2 inches from the surgical wound and hence difficult to completely block with a local injection. The vast majority of Spinal Surgeons have been ineffective in using this form of postoperative pain management.
2. Spinal anesthesia (antrathecal). If a spinal injection is done in or near the operative site, there is always a risk of spinal fluid leak into the surgical defect. This can lead to a post operative meningocele with the spinal fluid filling the surgical area. If this occurs chronic pain or additional operation(s) may be needed. If the spinal fluid leaked through the skin then meningitis with the risk of death can occur. Spinal anesthesia is clinically utilized for intraoperative anesthesia such as child birth and hip surgery. A separate puncture remote to the lumbar surgical incision has not been routinely used for postoperative pain management in an outpatient setting because of the risk of respiratory depression on a delayed basis.
3. epidural analgesia. An epidural anesthesia administered near the L1 to T10 area provides good anesthetic coverage of both lower extremities and the low back incisional region. This is the location of the spinal cord conus were the motor and sensory nerves to the legs connect to the central nervous system and anesthetic agents are most potent in pain relief for the legs and low back area. A combination of 2 cc's of Fentanyl (100 mcg.) and 8 cc of ¼% plain preservative-free Sensorcaine is just below a motor block and allows the patient to wake up pain free. The Fentanyl is believed to have a physiologic half-life of 1 to 2 hours and hence is not a threat for delayed respiratory depression as the longer acting narcotic morphine is known to occur in some cases. This epidural analgesia is typically supplemented with an addition injection of ¼% Sensorcaine into the skin just prior to skin closure in addition to before the initial skin incision. A patch of Fentanyl 50 mcg is placed on the skin and removed in three days. Oral medication as needed on a daily basis. NSAID medications are utilized preoperatively and postoperatively as per the surgeon's routine and the clinical situation.
Of the three extra analgesia options listed above, epidural analgesia uniquely provides the promise of completely blocking the onset of the pain spasm cycle following emergence form endotracheal anesthesia after the lumbar spinal surgeries while having an extremity low incidence of estimated side effects or additional surgical complications. However, epidural administration of analgesia via the lower lumbar surgical exposure after minimally invasive lumbar spine surgical procedures does present several technique challenges. Threading an epidural catheter intra-operatively in via the small lumbar incision to the L1 to T10 region is difficult even with a guide wire. Although the surgical identification of the epidural space is obvious intraoperatively, the catheter is threaded in a path that is at right angle to the surgical vision axis making it mechanically difficult to thread with the right angle bend necessary at the bottom of the wound. Ideal catheter position is to advance the tip of the catheter into the epidural space in the midline dorsal to the thecal sac 3 to 5 inches cephalad to the operative site (to the anatomic bony level between L1 to T10). The midline dorsal location is desired since there is usually a fat pad, and hence potential space, in this location along the whole spinal axis allowing an easy path for the catheter to be threaded. If the catheter path falls off the dorsal midline to one side of the spinal canal then the cephalad passage of the catheter is restricted or blocked by the laterally exiting nerve roots. Although it is possible to use an expensive CSF lumbar drainage catheter and advance it into this midline dorsal epidural space with a bayonet forceps, this technique is very cumbersome, technically demanding, time consumining, and requires extra midline bone removal. Also in some cases it is impossible to thread the catheter especially in the small minimally invasive lumbar spinal wounds.
The threading difficulty of the epidural catheter via a lumbar surgical wound arises from the need to thread the catheter at the bottom of the wound at an essentially right angle to the line of sight of the small surgical wound. The sharp angle of turn at the bottom of the wound combined with the catheter threading is beyond the surgical capability or patience of most spinal surgeons when current supplies and equipment are utilized. Thus, there is a need for a specialized system to aid the spinal surgeon in the rapid and reliable epidural catheter placement.